The present invention is directed to a down hole tool, and more particularly to an oscillating mud motor to provide rotational reciprocation for a reamer shoe.
In oil and gas exploration and production operations, bores are drilled to gain access to subsurface hydrocarbon-bearing formations. The bores are typically lined with steel tubing, known as tubing, casing or liner, depending upon diameter, location and function. The tubing is run into the drilled bore from the surface and suspended or secured in the bore by appropriate means, such as a casing or a liner hanger. For a casing, cement may be then introduced into the annulus between the tubing and the bore wall.
As the tubing is run into the bore, the tubing end will encounter irregularities and restrictions in the bore wall, for example ledges formed where the bore passes between different formations and areas where the bore diameter decreases due to swelling of the surrounding formation. Further, debris may collect in the bore, particularly in highly deviated or horizontal bores. Accordingly, the tubing end may be subjected to wear and damage as the tubing is lowered into the bore. These difficulties may be alleviated by providing a shoe on the tubing end. Examples of casing shoes of various forms are well known in the art.
Another problem encountered is the difficulty of running casing through built sections. More specifically, there is difficulty in running large diameter casing through the build section of a well in moderate to soft formations. The stiffness of the casing requires a significant force that must be generated at the casing shoe to cause the casing to bend to follow the curved section of the wellbore.
Often times a reamer bit is attached to the bottom of a casing shoe for opening the hole in smoothing areas that may have ledges or under-gauge areas where the diameter of the hole is not large enough to allow passage of the casing. In certain applications a mud motor is incorporated to help operate the reamer shoe. Most mud motors have a progressive cavity power section which are not hollow but require drilling fluid to pass through the power section. This means that stalling the motor creates a pressure spike which can be detrimental to other pressure activated tools within the bottom hole assembly. Another problem with current wellbore liner and completion systems is that they require turning to the left or to the right a certain number of revolutions to set the hanger. By oscillating back and forth, current tools generate torque in both directions, but overall does not generate any net rotation so current tools would not turn the casing, liner or completion.
Mud motors are also incorporated into traditional drill strings including drill pipe and a drill bit, and they also suffer from the same problems when incorporated therein as in casing and liner configurations. Consequently a need exists for an improved mud motor design which addresses the problem of prior designs.